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smokey cab, where can it be coming from?


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well today I decided that I wanted to take my truck to work. it was a little chilly so I decided I should throw on the heat so I threw the heat to full hot left the fan on off (cause I'm dumb like that) and threw it on the defrost setting. so about 5 miles in I start to smell smoke, now I'm always paranoid about a fire in my truck, I repaired a burnt ground from the headlight switch that took out a couple wires along with it and it just has me worried about the other wires. but this smelled like burning wood or leaves, not electrical. so I put my window down and the smell seamed to get stronger so I though it was just a bonfire or something. well after about a 1/4 of a mile smelling it I started to see smoke coming from the dash. so I pulled off the road and killed the engine and started to look under the dash and under the hood to see if I could see anything. I didn't see anything so eventually I turned off the heat and drove it home and grabbed my car (didn't smoke on the way home).

now is there anything that is notorious for burning? I know the ignition will sometimes do it but this did not smell like wires melting. it was more like dried leaves. I do/did have a rodent problem (stinky vents like mouse urine and trapped a few :mad: ) so it may be a nest or something but what would produce that much heat in the under dash area? doesn't the heater just open a door and let in excess engine heat in? It may be in the engine bay but the majority of the smoke looked to be coming from the dash.

 

go figure this happens a couple days before I was going to bring it up to Vermonster4x4 and now I have to take my car again. but I guess its better then it happening on the way up or up there.

 

thanks for any info.

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If the fan was off, the resistor should not have gotten hot at all, I thought that too, but then he said the fan was off. I can't see the heater core getting hot enough to smoulder mouse house stuff either, but who knows.... definitely need to clean out what you can from the housing. Remove the fan and see what you find. When I swapped HVAC housings in my truck to add AC I had to remove all kinds of crap. If you can't get rid of the smell, that may be your only option (to pull the dash, remove the housing, and open it up to clean it out). Good luck.

 

OH and buy a good fire extinguisher!

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He said he was in defrost mode, in our trucks the fan is only off when the mode selector is in the off position, if he was in defrost, then the fan had to be at least on its lowest setting. So it still very well could be the resistor.

:agree: This.

 

"Off" is off. "Defrost" is not off -- the fan is running, and if the fan is not at high speed the current is going through one of the resistors in the resistor pack, so that's probably where the smoke was coming from.

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My Bronco did this once, and it was a small leak in the heater core under the dash. I hope that is not your problem, because in the Comanche it is a major undertaking to replace the heater core.

 

-Tom

:agree: I've had several vehicles that the cores went bad in. If you have a bad heater core, what your seeing isn't smoke. Its steam.
doesn't the heater just open a door and let in excess engine heat in?
No. When you set your climate control to heat, hot coolant/water from you engine circulates through the heater core. (a small radiator looking thing enclosed under the dash) Your fan then blows air across/through the core. With hot coolant/water going through the core, the air blown across/through it is what you feel as being warm air coming out of your vents. If your heater core has a small hole in it, your coolant/water will leak out as steam and as such come into the cab of your truck through the vents including the defrost vents. If you have anti-freeze in your radiator, the leaking anti-freeze in steam form will leave an oily residue on everything. If you had your climate control set on defrost, you will most likely have some of that residue in your defrost vents and on your windshield.

If the heater core is in fact your problem, the good news is your truck isnt going to burst into flames. The bad news is, not only is replacing the core a lot of work its also a pain in the Aaaaasssss.

The easiest temporary fix is to bypass your heater core by disconnecting your heater hoses and looping the system. More on that later if thats what you decide to do. If you bypass the heater core you will not have heat in your truck. Burrrrrrrrr.

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A quick check would be to pull the connector off the resistor, disabling it and the fan motor. Then warm up the engine and turn on the heater. If it still smells, then it's not something burning against the resistor. You could also remove the resistor and feel around in the hole with your finger to see if anything is touching it.

 

A hot water / antifreeze mix will smell skunky and moldy, and, as JACKED88 said, you will see steam coming from the vents or defrost.

 

-Tom

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well it definitely smelled like a leaf burning. and I have issues with rodents playing in my truck and before when i had turned on the fan and slapped the heater box under the pass side dash little tidbits of my seat stuffing and other paper/material like pieces would come out of the vents. my plan will be to pull the dash and heater assembly and clean it out. I could get all the crap out and possible get rid of some of the rodent piss smell. hopefully I can get it all done before it gets really cold, having no garage to work in sucks.

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my plan will be to pull the dash and heater assembly and clean it out.
If that was my truck and I intended to keep it for a while, there's No way I'd do all that work and not go ahead and replace the 20+,- year old heater core. :nuts:

 

BTW, although you may have a rodent issue and need to clean out their debris, there's just not enough heat created within the heater system or anything else under the dash to burn leaves. The heater being able to burn leaves would be like laying a dry leaf on top of your radiator and expecting it to burst into flames. Not gonna happen.

The only thing on an engine that will get hot enough to actually burn a leaf is the exhaust manifold/header pipes and possibly the first half of the exhaust system. Beyond the catalytic converter it's not really hot enough to burn anything but you. Melt? Yes. Burn? No.

Are you sure your little rodent buddies haven't built a nest on top of your exhaust? Try looking under the intake manifold on top of the exhaust manifold/header pipes. They seem to like it there. Also look on top of the exhaust pipe as far back as and including the catalytic converter.

 

It'll be interesting to know what you find. :dunno:

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BTW, although you may have a rodent issue and need to clean out their debris, there's just not enough heat created within the heater system or anything else under the dash to burn leaves. The heater being able to burn leaves would be like laying a dry leaf on top of your radiator and expecting it to burst into flames. Not gonna happen.

The resistors in the resistor pack get hot enough to burn leaves ...

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BTW, although you may have a rodent issue and need to clean out their debris, there's just not enough heat created within the heater system or anything else under the dash to burn leaves. The heater being able to burn leaves would be like laying a dry leaf on top of your radiator and expecting it to burst into flames. Not gonna happen.

The resistors in the resistor pack get hot enough to burn leaves ...

:doh: Your right. I forgot about the resister coils. That'll do it if his rodent buddies carried a bunch of who knows what in there.
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well it isn't a show truck so I was thinking that I could just cut a nice circle hole in the bottom of the heater box and reach up inside (with gloves) and clean it out. does anyone have a pic of a heater box and how it laid out on the inside so I know where to grab stuff? then I would find some plastic to bolt back in and seal it with rtv or something. thats just my idea, don't know if it will work.

 

oh and the smoke was pretty much only in the cab, I saw a little when I popped the hood but I'm pretty sure it was coming from a grommet that came off a little on the passenger side of the firewall. I did look around the exhaust manifold and didn't see anything.

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